The present invention generally relates to image forming apparatuses, and more particularly to an image forming apparatus capable of adjusting a tone of an image formed on a surface of a recording medium.
Recently, due to improved performances of information processing apparatuses, there are demands to improve the performance of image forming apparatuses such as printers. An image forming apparatus capable of forming an image having a gradation representation on a recording medium such as paper has been developed to satisfy such demands.
Conventionally, image forming apparatuses capable of forming monochrome or color images having the gradation representation on the recording medium have been proposed. Particularly in the case of a color image, if the tone of each color is different from a corresponding designed value, the quality of the image formed on the recording medium greatly deteriorates. Hence, a method has been proposed to control a density of a toner image by detecting the density of the toner image and feeding back the detected density to an image forming part. According to this proposed method, an optimum value of the density of the toner image with respect to a certain image tone data is set in advance, and an amount of error of the density of the toner image which is actually formed from the optimum value is obtained based on this certain image tone data. When forming the image thereafter, the amount of error is added to the image tone data as an offset value, so as to correct inconsistencies in image forming characteristic of each of the individual image forming parts.
However, the amount of error of the density of the toner image which is actually formed from the optimum value is not constant and differs depending on the tone. For this reason, according to the proposed method which adds a constant offset value to the image tone data, there was a problem in that it is impossible to accurately reproduce all tones.
In the case of a monochrome image, even if the density of the toner image is slightly deviated from the designed value, this deviation is not conspicuous in the image which is formed on the recording medium. But in the case of the color image, even if the density of the toner image of one color deviates from the designed value, the color in the image which is formed on the recording medium becomes unnatural, thereby greatly deteriorating the quality of the image.